Improved simulation of plant-animal interactions in African savannas with the extended land use change model LUCIA

Process-based modelling is needed to assess potential ecological impacts of large-scale intensification of African savanna rangelands and to investigate major processes involved, that cannot be tested on appropriate temporal and spatial scales at field level. To date, modelling conversion or integration of crop- and pasture-based systems in savanna ecosystems is not possible at the necessary level of detail. The Land Use Change Impact Assessment tool (LUCIA) dynamically simulates spatially explicit impacts of land-use change on ecosystem functions within a grid-based landscape. We added a physiologically detailed source-sink plant growth module with growth reserves, dynamic biomass partitioning, and dormancy to LUCIA to simulate a grazed rangeland vegetation in Borana, Ethiopia. Grass and tree growth, validated against measured above-ground biomass time series were most sensitive to dormancy break or induction parameters that control the growing period under strong rainfall seasonality. A moderate stocking rate of cattle allowed pasture persistence and continuous fodder production. Overgrazing caused depletion of root and tree stem growth reserves that were needed for seasonal regrowth. Consequently, pasture degraded due to reduced regrowth capacity and reserve replenishment. Physiological processes are well represented, laying the foundation for integration of further ecological processes, such as tree recruitment, bush encroachment, and plant community shifts.